Digital distortion-correcting circuit for projection a flat image on a curved screen from a digital data source for a simulator projected-image visual system

ABSTRACT

A simulator projected-image system includes a distortion-correcting circuit to modify flat-image data that is stored sequentially in a Random Access Memory by connecting a source of random address to obtain selected video data from the memory in a predetermined order and a circuit to combine the selected video data to form an image that is substantially free from distortion when projected on a curved screen.

BACKGROUND

The present invention, generally, relates to a projected-image visualsystem as used in a simulator and, more particularly, relates to adigital distortion-correcting circuit for projecting a flat image on acurved screen in such a visual system.

Visual scenes that are viewed in the real world are simulated byprojecting images from a video source onto a screen.

For large fields of view (FOV's), generally the screen surface is curvedwith the projection optics projecting over a wide angle.

The video output, which usually consists of a database transformed ontoa flat image plane, must be processed by a suitable electronic systembefore it is projected onto a curved screen surface.

It is this processing function that is required of the electronic systemthat the present invention is concerned. This processing function istermed "mapping" in the art.

"Mapping" is defined as changing the output video elements from theimage source such that the inherent time relationships of the elementsis not equivalent to the resultant spatial relationships on theprojector plane.

"Mapping" is required in the electronic system for three basic reasons,including (1) nominal design, (2) manufacturing tolerances, and (3)drifts. There are elements of a nominal system which require "mapping".The digital image source compensates for the fact that both theprojection and the viewing point are not at the same center.

However, the image source can only produce "mapping" which is suitablefor projection on a flat screen by a special-purpose projector. Inaddition to the mapping requirement identified above, thespecial-purpose projector has some sweep non-linearity inherent in itsnominal design that requires some "mapping" correction.

Several elements of the visual system are subject to manufacturingtolerances to a sufficient degree that an alignable "mapping" correctormust be utilized to reduce distortion to acceptable levels. Examples ofthese include projector sweep non-linearities, wide-angle lens systemgeometric distortion, and spherical screen radius.

The "mapping" that is required in the environment described above isprovided by the distortion-correcting circuit of the present invention.

INVENTION OBJECTS AND SUMMARY

Accordingly, it is an important object of the present invention toprovide a distortion-correcting circuit that will effectively correct aflat image that is projected onto a curved screen without introducingdistortion.

It is a further object of the invention to provide such a circuit thatis effective in a digital environment.

It is another object of the invention to provide such a circuit that iseffective in any image source for providing a perspectively correctimage on a curved screen.

Broadly, a digital video mapping circuit constructed and arranged inaccordance with the present invention provides a first means to storevideo data. The circuit of the invention has also a second means tostore random addresses to obtain from the first means selected videodata in a predetermined order, and a third means to combine the selectedvideo data to form the mapped image, so that a pre-distorted image isprojected onto the curved screen in such a manner that it will appearcorrect to a viewer in the operator's position of the simulator.

THE DRAWINGS

In the accompanying drawings, forming a part of this specification, inwhich like numerals identify like parts in the various figures:

FIG. 1 is a block diagram of a digital distortion-correcting circuitthat is constructed and arranged in accordance with the invention;

FIG. 2 is a block diagram showing the details, interconnections, andarrangement of respective component parts to make up the invention shownmore broadly in FIG. 1; and

FIG. 3 is a block diagram showing one of the component parts that makeup the plurality shown in FIG. 2.

INVENTION DETAILS

In a simulator visual system where images are projected over substantialdistances onto a large curved screen, such as a dome, there are severalreasons why distortion appears to exist. One of these reasons is thatthe operator is viewing the image from a different position from thatwhich the image is projected. Another is that an image constructed to beprojected onto a flat screen 12b will appear distorted when projectedonto a curved screen 12g. An example of this is a straight line whichwill appear as a straight line on a flat surface, but will appear curvedwhen projected on a curved screen.

A circuit that is constructed and arranged in accordance with theprinciples of the present invention contemplates predistorting the imageso that when it is projected onto a curved screen, it will appearvisually correct and undistorted. The circuit of the present inventionoffers a new and improved way of accomplishing the predistortingfunction.

Referring now to FIG. 1 of the drawings, an image generator 10 can beany suitable source of video data, such as a computer image generator, avideo camera or a graphics generator (for providing a suitable testpattern). The digital data provided by the image generator normallywould be converted to analog form by a digital-to-analog converter 11.The analog signal, then, is used to drive a 1,000 lumen light-valveprojector, such as, for example, G. E. P/N 5155. Such a light-valvevideo projector is identified in FIG. 1 of the drawings by the numeral12.

This same digital visual image generated by the source can now, with thecircuit of the present invention, be projected onto a screen that iscurved. Before proceeding with a detailed description of the operationof the circuit in accordance with the invention, a broad, generalexplanation will be presented.

The visual image in digital form as generated by the generator 10 isconnected directly over a line 13 to a memory buffer 14 where it isstored sequentially. A separate line 15 is used to connect a series ofclock pulses to the memory buffer 14 to maintain the same clock rate.

While the visual image data is stored in the memory buffer 14sequentially, it is read out at random under the control of a correctionfunction generator 16, as will be explained in more detail in connectionwith FIG. 2 presently. This control from the correction functiongenerator 16 of the visual image data stored in the memory buffer 14 isin the form of address control signals over a bus 17.

The randomly selected video data from the memory buffer 14 is connecteddirectly over a line 18 to a data processor circuit 19. As the selectedvideo data proceeds through the data processor circuit 19, theillumination factor for each pixel receives a supplemental weightingcoefficient applied to it over a bus 20 from the correction functiongenerator circuit 16.

The output from the data processor circuit 19 is connected directly overa line 21 to the digital-to-analog converter circuit 11, the analogsignal output of which is connected over a line 22 to the light-valvevideo projector 12. The operation of the correction function generatorcircuit 16 is maintained in timed relationship with the projected imageby means of a connection 23 for a clock reference signal from thelight-valve video projector 12.

In FIG. 2 of the drawings, a line addresses circuit 24, an elementaddresses circuit 25 and the two coefficients circuits 26A and 26B areindicated, by the broken line 27, as being all of the correctionfunction generator 16, in FIG. 1. The memory buffer circuit 14, in FIG.1, is indicated in FIG. 2 as being a plurality of individual RandomAccess Memory units (RAM). The data processor 19, in FIG. 1, is shown inFIG. 2 as including a plurality of individual multiplier units and aplurality of adder units with two input connections 18 and 20 and with asingle output connection 21.

One of the Random Access Memory circuits within the memory buffer 14 isidentified by the reference numeral 28 as having two output linesidentified by the reference numerals 29 and 30, respectively. The outputline 29 is connected by the bus 18 to a multiplier circuit 31 within thedata processor 19, and the output line 30 is connected, also by the bus18, to a second multiplier circuit 32 within the data processor 19.

Each of the two multiplier circuits 31 and 32 have respective outputlines 33 and 34 connected as the two input lines to an "adder" circuit,identified in FIG. 2 by the reference numeral 35. The "adder" circuit 35in FIG. 2 has a single output line 36.

Reference is made now to FIG. 3 of the drawings for the purpose ofexplaining, in still further detail, the circuit shown in FIG. 2. InFIG. 3, the Random Access Memory circuit (or "RAM"), identified also bethe reference numeral 28, is shown with a plurality of input lines. Theline with the legend "CL(OUT)" is for controlling the data rate out thatis randomly selected by the correction function generator 16 over thebus 17 as explained previously.

The input line with the legend "CL(IN)" is a connection for receiving aclock rate for controlling the data input as it is stored sequentially.The two lines with the legends "CNTR (EL)" and "CNTR (LN)",respectively, indicate the Element Counter signals and the Line Countersignals for the data stored sequentially in the RAM 28. The two lines inwith the legends "AO (EL)" and "AO (LN)", respectively, identify the"Element Address" signal input and the "Line Address" signal input, alsorespectively.

There are six timing lines that control the Random Access Memory circuit28, and these are identified with the legends "MNE/MNO, which identifythe Memory No. Even/Odd lines. The single line with the legend "WP" isfor the Write Pulse signal, and there are three lines with the legends"MNR/WC" which identify the Memory No. Read/NOT-Write control lines.

The various legends indicated within the Random Access Memory circuit28, in FIG. 3, are for the purpose of identifying one suitable addressmethod for storing data in the memory 28. Of course, other suitableaddress legends may be adopted, if desired.

Since the light valve video projector 12, FIG. 1, is capable ofcompleting a frame of projected information in one-thirtieth of a secondonly, and since the operating speed limitations of the respectivecomponents shown in the circuit of FIG. 2 is only one-sixtieth of asecond, two circuits of the type shown in FIG. 2 are connected tooperate in parallel, one for each of two fields per one frame ofprojected image. Of course, as technology advances and components withfaster operating speeds become available, perhaps it will be possible toutilize only a single one of the circuit arrangements of FIG. 12.

While the preferred embodiment of the present invention has been shownand described in detail, it is apparent to those skilled in the art thatmodifications and changes may be made without departing from the spiritof the invention and the scope of the claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined in the claims appended hereinafter.

We claim:
 1. In a simulator projected-image visual system, adistortion-correcting circuit to modify a flat image for projection on acurved screen to produce an image that is substantially free fromdistortion, comprising:random access memory means including connectionsfor storing video data sequentially and for accessing stored video datarandomly to represent a predetermined undistorted image when projectedon a flat screen; means to store random addresses to obtain selectedvideo data from said random access memory means in a predeterminedorder, and means to modify said selected video data by combining with adata signal representing a predetermined weighted average to form saidimage that is substantially free from distortion when projected on acurved screen.
 2. A distortion-correcting circuit according to claim 1including a source of video data separate from saiddistortion-correcting circuit for generating said flat image, andincluding bus means to connect said video data to saiddistortion-correcting circuit.
 3. A distortion-correcting circuitaccording to claim 2 wherein said video data from said source is digitalin form, and a digital-to-analog converter means to convert saidcombined video data to analog form.
 4. A distortion-correcting circuitaccording to claim 3 including video projector means connected toreceive the output from said digital-to-analog converter means.
 5. Adistortion-correcting circuit according to claim 4 wherein said videoprojector means is in the form of a light-valve video projector toreceive said output from said digital-to-analog converter means.
 6. Adistortion-correcting circuit according to claim 1 wherein said means tomodify said selected video data includes a plurality of multipliercircuit means.
 7. A distortion-correcting circuit according to claim 6wherein said multiplier circuit means has two input connection means,one to receive said selected video data and the other to receive saidweighted average data signal.
 8. A distortion-correcting circuitaccording to claim 7 wherein said multiplier circuit means has a singleoutput connection means.
 9. A distortion-correcting circuit according toclaim 8 including a plurality of ADDER circuit means, each connected toreceive said weighted average data signals from two multiplier circuitmeans.
 10. A distortion-correcting circuit according to claim 1 whereinsaid random access memory includes connection means to receivepredetermined address signals to identify the video data to be selected.11. A distortion-correcting circuit according to claim 10 wherein saidrandom access memory includes a plurality of separate connection meansto receive said predetermined address signals.